F-22 Raptor Manufacturing
If building an aircraft that has been described as "the only thing more complex than the human body" in five separate geographic locations wasn't challenge enough, the F-22 team also has to build an aircraft to tolerances on the order of ten-thousandths of an inch in order to meet its stealth requirements. Certainly not an easy assignment.
But the initial hurdles have been overcome. When the first F-22's fuselage was mated in the fall of 1996, the pieces went together just as the designers had predicted they would. Final mate of the forward fuselage that was made in Marietta, Ga., to the mid fuselage made in Fort Worth, Texas, and that mid fuselage to the aft fuselage made in Seattle, Wash., took only a few days to accomplish. The first shipset of wings was mated in less than 48 hours. The vertical stabilizers went on in less than a day. Between the two body mates and the wing joins, a total of 40 shims had to be generated, all about the thickness of a sheet of paper.
The Integrated Product Team (IPT) philosophy that the F-22 and F119 are being developed under has paid big benefits in the manufacturing area. The IPT concept has moved manufacturing from its traditional place down the schedule to up front with the designers. Manufacturers worked with designers and maintainers to ensure that a part or system was not only designed correctly, but it could be manufactured, and it could be maintained while that part or system was still on the drawing board.
While not a revolutionary idea, collocated IPTs does make good common sense. It improves communication and avoids problems and rework later on.
The computer revolution has changed the detail design process of the aircraft. With the IBM-Dassault Systemes-designed Computer Aided, Three-Dimensional Interactive Application (CATIA), the aircraft designer can design the parts of the F-22 as a solid object, not just lines on a flat page.
With COMOK (a team-developed computer mockup simulation), the designer can visualize every aspect of the design including complex routing for wires, tubes, and cables. There is no 'hard' mockup of the F-22.
These computer programs allow the design engineer and the manufacturing engineer actual look inside the structure before it is built.
More than just a visualization, the computer data that creates these images are precisely stored design measurements that can be transferred, again by computers, between the team's locations in Marietta, Ga., Fort Worth Texas, Seattle, Wash., and West Palm Beach Fla., and East Hartford, Conn. and supplier locations all around the country.
Parts of the aircraft fit remarkably well when received in Marietta, where final assembly takes place, even though no master tool was sent to trial fit the pieces. In fact more than 270 master tools have been eliminated as confidence in the 3-D tools grew. As part of the IPT process, the team found that it could hold tolerances to 1/6000 of an inch on parts.
The numerical control (NC) machines that mill the parts for F-22 use the same data set as the CATIA design tools, and there are no errors in translation between the two. So, by removing variation in the data set, one-half of the possibility of variation between parts is eliminated. The possibility of variation because of the machine fabricating the part remains, however.
The F-22's avionics have the computing power of two Cray supercomputers, and they produce a large amount of heat. The racks that hold the avionics are not only thermal management units - the F-22's avionics are air cooled, liquid cooled, and liquid flow-through cooled, they are also structural parts of the aircraft. The racks have to hold the modules in the correct position in the backplane and they cannot leak, even when the aircraft is maneuvering violently at forces up to nine-Gs.
More than 250 avionics racks had been built as of early 1997, out of a total of just under 300 racks necessary for the current Engineering and Manufacturing Development (EMD) phase of the program. The avionics racks are fabricated and assembled in Marietta, Ga.
Unlike many other aircraft programs, where parts move from tool to tool, a majority of F-22 tools move with the part. This keeps the part from flexing or not being aligned properly when it is moved to the next tool in the assembly process.
The F-22 tooling is also designed to be as ergonomic as possible. The tools are elevated to allow workers to get under them without stooping and they are well lit. In final assembly, the workstands move on integral castors to allow them to be pushed easily against the aircraft.
The final assembly line in Marietta is sized for producing the EMD aircraft and the F-22s in the low-rate production lots. At high-rate production (48 aircraft per year), it would only be necessary to add duplicates of some of the existing tooling. The team's design goal was to build the first EMD aircraft as closely as possible to the first production aircraft
Composite tools for building composite parts are not durable, so the team opted to build Invar steel tools. This allowed for tools that can be reused over and over. The Invar tools contain all the necessary thermocouples for measuring the temperature of the part, and the necessary connections are also all in one place.
Of the composite parts produced for the first aircraft and those following after, as an example, Lockheed Martin Aeronautical System achieved a 90% usable first part yield, and 78% of the parts were defect-free. Most of the defects were found using non-destructive inspection (NDI) and could be corrected.
The aft fuselage of the F-22 is mostly high strength titanium, as it has to hold the aircraft's F119 engines, and it must be able to withstand the high temperatures the engines create. The mid fuselage transitions from titanium (in the larger, load-bearing bulkheads) to forged aluminum bulkheads and aluminum frames. The forward fuselage contains a composite fuel tank (the F-1 tank behind the pilot's ejection seat) and is made of machined aluminum. The wings are made of composite spars and skins with titanium reinforcement.
Two computerized systems that have been implemented at Lockheed Martin Aeronautics Company in Marietta are being utilized in the process of assembling the F-22, DASS and MATS.
The Dynamic Assembly Scheduling System (DASS) is a simulation of the entire factory. A manager loads in data - who is out sick, what tools are down for maintenance, etc. - and the system runs a simulation of the work day and it then resequences the work to what can be done on that particular day.
The Manufacturing Assembly Tracking System (MATS) is a television-sized monitor that allows the individual worker to call up the work task for the day and the system provides the instructions to accomplish it. The worker can look at diagrams of the procedure and can zoom in to look at specific parts. A temporary drawing can be printed if necessary, but the drawing is discarded at the end of the day. That way, only the most current drawing is used. The MATS terminal also serves as an electronic bulletin board, allowing workers to view current news, company staff meeting notes, etc.
In the Final Assembly Area, workers are not allowed to use the "own" tools. All of tools are shadowboxed in company-issued toolboxes and when a worker removes a tool, he or she places a chit with a photograph and the employee's number on it in the tool's slot. All of the tools are accounted for at the end of each shift and the boxes are locked until the next shift comes in. This eliminates the possibility of a tool being left in the F-22 and creating a Foreign Object Debris problem.
F-22 AIR VEHICLE COMPONENTS
Lockheed Martin Aeronautics Company in Marietta, Ga. builds the forward fuselage of the F-22. It consists of the structure aft of the radar bulkhead, the cockpit area, nose wheel well, and F-1 fuel tank. It consists of approximately 3,000 parts made mostly of aluminum and composite materials. The forward fuselage also contains wiring harnesses, tubing, cockpit instrument fixtures, avionics racks, and canopy mounts.
The F-22's forward fuselage is just over 17 feet long, slightly wider than five feet inches wide at its widest point, five feet, eight inches tall, and weighs roughly 1,700 pounds.
Built up in two sections, the forward fuselage is joined together by two long and relatively wide side beams and two longerons that run the length of the assembly. The beams, made of composite material, also provide an attachment point for the F-22's chine, a fuselage edge that provides smooth aerodynamic blending into the intakes and wings. The 17-foot-long aluminum longerons form the sills of the F-22's cockpit and the canopy would rest on them.
The canopy is also built up in Marietta, and is approximately 140 inches long, 45 inches wide, 27 inches tall, and weighs approximately 350 pounds. Seven test canopies were built for the sled test program.
The integrated forebody, also referred to as the radome, is composite. It is manufactured by Lockheed Martin Aeronautics Company in Palmdale, Calif.
The empennage consists of the vertical and horizontal tails. The verticals are a multi-spar configuration internally, and with a hot isostatic pressed (HIP) cast rudder actuator housing. The edges and rudder are made of composites., and both parts have embedded VHF antennas, as well as other antennas. The rudders can also be towed inward to act as a speedbrake for the F-22.
The horizontal surfaces, known as stabilators, are made of honeycomb materials with composite edges. They are all-moving assemblies and are deflected by the Composite Pivot Shaft (see CPS in Materials and Processes section).
The mid fuselage is the largest and most complex of the F-22 assemblies. It is approximately 17 feet long, 15 feet wide, and 6 feet high, and weighs approximately 8,500 pounds as shipped.
The mid-fuselage is considered the heart of the F-22 as almost all systems pass through this section, including the hydraulic, electrical, environmental control, and auxiliary power systems, as well as the aircraft's fuel. In addition, there are three fuel tanks, four internal weapons bays (the two side bays, and the two sections of the main weapons bay that is separated), the 20-mm cannon, and the auxiliary power unit (APU).
Mid fuselages of F-22 EMD aircraft are assembled in the north end of the Lockheed Martin Aeronautics Company in Fort Worth, Texas. Employees at the Fort Worth plant fabricate most of the composite parts and assemblies, tubes, and harnesses in the mid fuselage.
Most of the aluminum machined parts are made by Lockheed Martin Aeronauticsl Company in Marietta, Ga. Subcontractors spread throughout the United States supply titanium parts, standard hardware, and system components for the mid fuselage.
Lockheed Martin is using a modular approach to assemble the mid-fuselage. Three modules, which are simultaneously assembled prior to mating, make up the mid-fuselage structure. This modular approach provides greater efficiency and access to the densely packed mid fuselage structure.
A unique tooling process assembles each module vertically, which helps fit parts in the high tolerance locations of the mid fuselage. An elevator that runs in the air inlet ducts provides access within the structure. The modules are then switched to the horizontal position for mating. The initial vertical assembly provides optimum manpower to the module, decreasing the overall assembly span time, which translates into significant dollar savings.
Like the entire aircraft, the F-22 mid-fuselage was developed in an Integrated Product Team (IPT) environment. Members of the teams include personnel from various disciplines. The process has worked extremely well for the program, resulting in a significant decrease in engineering changes and scrapped parts.
The composition of the F-22 airframe uses a unique combination of materials to provide the best cost and weight balance. Unlike conventional aircraft, only 35% of the F-22 mid fuselage structure is aluminum. Composites make up 23.5% and titanium is nearly 35%. One of the four one-piece titanium bulkheads is the largest single piece of titanium ever to be used on an aircraft.
This optimum mixture was the result of extensive material trade studies that evaluated cost and weight benefits of various design, material and manufacturing concepts. A critical part of these studies was an extensive analysis of thermal expansions that can induce significant stresses into the airframe This study reduced the risk that is normally associated with use of multiple materials in airframe design.
Because of its width, the mid fuselage has to sit at almost a 45-degree angle in its reusable metal shipping container. This is so its shipping box would fit on a flatbed truck and still be allowed on roads from Texas to Georgia.
Boeing began major assembly of the aft fuselage for the world's first F-22 in June 1996 at its Developmental Center in Seattle, Wash. Boeing began the process by loading the left-hand forward boom, a large component that contains fuel and carries structural loads, into the aft fuselage assembly fixture.
The F-22 aft fuselage houses the two Pratt & Whitney-built F119 engines that power the F-22. It also contains all or part of the aircraft's environmental control system and fuel, electrical, hydraulic, and engine subsystems. The aft fuselage is designed to withstand supersonic speeds for extended periods of time and extremely 'high-g' maneuvers.
The aft fuselage is 67 percent titanium, 22 percent aluminum and 11 percent composite by weight. A completed aft fuselage weighs 5,000 pounds and measures 19 feet long by 12 feet wide.
Approximately 25 percent (by weight) of the aft fuselage is comprised of large electron beam welded titanium forward and aft booms. The largest of these booms, the forward boom, is more than 10 feet long and weighs approximately 650 pounds The welded booms of the aft fuselage are extremely weight-efficient and reduce the use of traditional fasteners by approximately 75 percent.
The aft fuselage is shipped to Marietta in a reusable metal container that fits upright in a rail car, or can be placed on its side for shipping by cargo aircraft. The first aft fuselage was delivered to Marietta aboard a Lockheed-built C-5 Galaxy.
Boeing began assembly of the left-hand wing for the first F-22 in January 1996 when machinists loaded wing attachment parts for external fuel tanks and weapons pylons into an assembly tool.
By weight, the Boeing-built portion of the wing is 42 percent titanium, 35 percent composite, and 23 percent aluminum, steel, and other materials in the form of fasteners, clips, and other miscellaneous parts. Each wing weighs approximately 2,000 pounds.
Each of the wings measures 16 feet (side-of-body) by 18 feet (leading edge) and is roughly triangular in shape. The wings together give the F-22's planform a modified delta shape. The wings are designed to cruise at supersonic speeds for extended periods of time and withstand extremely 'high-g' maneuvers.
The wings incorporate structural design modifications made early in the development program. After analyzing the results of live-fire tests simulating severe combat damage, engineers chose to reinforce the wing by replacing every fourth composite spar with one made of titanium. The titanium reinforcements ensure that the F-22 would be more survivable in combat. The wings are designed to be interchangeable from airplane to airplane.
Principal suppliers to Boeing on the wing include Dow-United Technologies of Wallingford, Conn. (composite sine wave spars); Howmet of Norfolk, Va. (side-of-body rib and aileron support castings); Schlosser of Redmond, Ore. (pylon rib castings) and Curtiss Wright of Fairfield, N. J. (leading edge flap drive system).
The wing shipping containers are designed to transported either by rail (the preferred method) or by transport aircraft. The wings for the first F-22 were shipped to Marietta via Air Force transport aircraft.
SPECIALIZED MANUFACTURING AND
FINAL ASSEMBLY FACILITIES
The F-22 factory at Boeing introduces the use of an automated, laser-guided machine for drilling holes in components where fasteners are still required.
Originally developed for the B-2 bomber program, the system uses a laser tracker with a targeting feature and automated data feedback software to guide the drill to exactly the correct location before drilling, It does so by measuring the relative position of the drill to the structure and automatically making positional adjustments.
Operated by machinists, the system drills nearly 2,500 holes into the aft fuselage structure. The location, size, and depth of the holes are controlled by engineering data fed into a computer. The holes are used for attaching the upper composite skins and lower engine-bay doors to the aft fuselage structure.
Precision drilling is also being used to drill 14,000 holes in each F-22 wing set as well, which allows for attachment of the composite wing skins to the titanium and composite substructure.
Final assembly operations for the new fighter took place in the 3.5-million-square-foot B-1 building (which has been in near-continuous use since 1943) at Lockheed Martin Aeronautics Company in Marietta. However, other things necessary for the F-22 specifically - such as composite parts fabrication, painting, radar cross section verification, ground-based engine runs, and flight operations - take place in nearly $31.5 million worth of facility improvements. Most of the facilities improvements are located near the company's flight line.
The largest of the new buildings is the radar cross section (RCS) verification building. This 50,000 square-foot fully enclosed structure was used to test the 'stealthiness' of each F-22 when it comes off the assembly line.
The main section of this building feature a 45-foot-diameter turntable with precise positioning capability that allow for testing of full-size aircraft. This section of the building measure 150 x 210 feet and 45 feet high. The facility had a separate 60 x 210 foot anechoic chamber for aircraft antenna testing.
Burns & McDonald Engineers of Kansas City, Mo., designed the structure. It is expected to be operational by late summer 1997.
The other new building in Marietta to support the F-22 is the robotic coatings facility. This 43,000 square foot facility, which is fully compliant with all environmental regulations, will have separate areas for materials handling, subassembly painting, and a large bay where most of the exterior of the aircraft was painted.
Two robotic painting systems were used in the building, which were designated as L-64 ('L' indicates a Lockheed Martin-owned building, '-64' is the next available number). The subassembly painting area utilized a small, six-axis spray-head robot mounted on a 25-foot long track. This robot was used to paint parts such as panels, doors, and the F-22's control surfaces before those parts are installed on the aircraft.
The aircraft's exterior will be painted with a standard six-axis spray head mounted on a hydraulically-operated arm that can be raised and lowered and is, itself, attached to a movable platform. This wire-guided platform, called an Automated Guided Vehicle (AGV), features electric drive wheels and hydraulic stabilizing jacks and was positioned at several points around the aircraft as it is being painted.
The large robot has 28-foot horizontal reach and the spray head can be raised as high as 26 feet. The large robot, developed by Pratt & Whitney Waterjet, Inc., is an offshoot of the Large Aircraft Robotic Paint Stripping (LARPS) system developed under the Air Force's Manufacturing Technology (MANTECH) program for the Oklahoma City Air Logistics Center at Tinker AFB, Okla.
The robot's software will be verified on a full-scale mockup of the F-22 called the Finish Application Mockup (FAM), rather than risk an aircraft. The highly realistic FAM includes panel lines and sits at exactly the same height as the real aircraft. Once the paint robot's software is proven, the FAM was used to test the systems in the RCS Verification Building.
The large robot allows for precise application of the aircraft's paint. Unlike many other aircraft, where a base coat is applied over the entire aircraft, and then the camouflage coat is added on top of that, the F-22's two-tone camouflage scheme of dark gray on a light gray was actually be applied separately.
The robot first painted the light gray surrounding what will be a camouflage area, but left a hole where the dark gray would go. It then went back and added the dark gray. This saved paint, and more importantly, didn't add additional weight anywhere on the aircraft.
L-64 measured 90 x 100 feet and cost approximately $16.5 million (including the robots). Choate Construction of Atlanta was the prime contractor and operations began in the building in late 1996.
A third new facility on the Lockheed Martin flight line wasn't actually new at all. The engine noise attenuation facility (more commonly known as a 'hush house') was used for ground-run tests of each F-22's twin Pratt & Whitney F119-PW-100 engines was formerly located at McConnell AFB, Kan.
The facility, designated B-22 (the 'B' indicates a government-owned building) was disassembled, trucked to Marietta, and reassembled across the ramp from both of the other new buildings. Vita-Link was the prime contractor for the move, and Burns & McDonald provided engineering support.
One feature unique to high-performance aircraft is ejection seats. In order to safely store and handle the pyrotechnics necessary for the F-22's ACES II ejection seats, the existing B-66 building was modified. This small building, which was formerly used to monitor C-5 ground engine runs, is of sturdy construction (thick walls, etc.) and would contain an explosion should one occur.
The final major facility upgrade on the flight line was improvements to the existing L-10 building. This building houses flight test (and later production flight) operations for the F-22. The building would have the necessary utilities to support four aircraft at the same time. Pratt & Whitney also had an engine buildup and repair area. Control room and locker area space were also included.
The facility improvements for F-22 also took place in several other buildings of the Air Force-owned, Lockheed Martin-run plant. Office and Integrated Product Team support spaces for F-22 manufacturing personnel were constructed in the main B-1 building near the F-22 assembly line in 1995. This project was one of the first undertaken.
Another project completed in 1995 was activation of the composite parts fabrication area in the existing L-11 building, which was once used for assembly of JetStar executive transports.
The final major facilities improvement at Lockheed Martin Aeronautics Company was the renovation of the B-4 building, which is located near the B-1 main assembly building. Two non-flyable F-22 airframes (the static and fatigue test articles) underwent ground testing in one high bay of this building, and, in order to accomplish those tests, a new hydraulic system was installed.
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